Alkylaryl sulfonates have been recognized as promising for enhanced oil recovery by surfactant floods. They can be manufactured in large quantities and can generate low interfacial tensions with oils under favorable conditions, see Malmber, E. "Large scale sulfonates for laboratory studies in tertiary oil recovery:preparation and related studies, final report" USDOE report No. FE-2605-20, May 1979. Much of the efforts have been to develop unique, monomerically pure surfactants for light oils, see Malmber, E. W. et. Al., "Characterization and oil recovery observations on a series of synthetic petroleum sulfonates," SPEJ (April 1982) 226-236; and Comberiati, J. R., et. Al., "Increasing the EOR activity of certain synthetic alkylaryl sulfonates," DOE/METC/TRP-83-3, November 1982.
While pure alkylaryl sulfonates, such as hexadecyl benzene sulfonate, can generate adequate phase behavior and low interfacial tension with light alkanes, they are unsatisfactory when dealing with heavier crude oils, particularly those with a high wax content. They do not form normal phase behavior when mixed with crude oil and brine of varying salinity. At low salinity, surfactant predominantly stays in the aqueous phase, forming a lower-phase microemulsion; at high salinity the surfactant predominantly stays in the oil phase, forming an upper-phase microemulsion. As noted in Improved Oil recovery by Surfactant and Polymer Flooding, Academic Press, 1977, normally, a surfactant-oil-brine system that has high oil recovery potential exhibits a lower- to middle- to upper-phase microemulsion transition as salinity increases. Near the mid-range salinity, often termed optimal salinity, a middle-phase microemulsion forms with appreciable amount of oil and brine solubilized in the microemulsion phase. However, if the oil contains a significant fraction of wax, the above phase transition often does not occur and the solubilization capacity is low, resulting in high interfacial tension and poor oil recovery capability.
Additionally and especially with low oil prices, the surfactant must be cost effective. Prior methods which use narrow selections of carbon chain lengths increase the cost because of the large quantities of unsuitable byproducts and/or the need for more tightly controlled reactor conditions or specialized catalysts.
Thus highly desirable would be to have a recovery process and composition useful in waxy crudes. Also desirable would be to have a composition which usefully includes a broad spectrum of carbon chain lengths so substantially complete production runs can be used.